I have been struggling trying to get calibre-portable.bat to work. I keep getting the error "Python function terminated unexpectedly [Error 3] The system cannot find the path specified: u" (Error Code: 1). I have done an extensive amount of debug on this and have narrowed it down to one line in the batch file. The very last one:
START Calibre --with-library "%CALIBRE_LIBRARY_DIRECTORY%"
Everything works fine up until I hit this line. Prior to this line I checked to make sure my variables are correct
Echo %CALIBRE_LIBRARY_DIRECTORY% returns correctly Z:\
The other variable I set is CALIBRE_OVERRIDE_DATABASE_PATH and that is also set correctly.

Next the head scratcher. I tried to use cmd window and entered:
START Calibre --with-library "%CALIBRE_LIBRARY_DIRECTORY%"
and it worked fine. Variables were configured the same.

I tried just creating a batch file with just
START Calibre --with-library "%CALIBRE_LIBRARY_DIRECTORY%"
Verfied the variables were correct using cmd prior to executing the batch file same error...bizarre. Please Help.

My book files are located on a shared drive on my networks. Which I have mapped to drive Z:/ on my laptop.

I have the metadata.db stored locally on the laptop. I have a lot of books and the metadata.db file is quite large. Storing locally will enable me to open Calibre much faster then if I were to access it over the network. Yes, I do know to occasionally update it when I add new books.

My book files are located on a shared drive on my networks. Which I have mapped to drive Z:/ on my laptop.

I have the metadata.db stored locally on the laptop. I have a lot of books and the metadata.db file is quite large. Storing locally will enable me to open Calibre much faster then if I were to access it over the network.

That is a great reason to use the batch file. Is this for a portable install? If not just hard code the exact path and try again.

If that doesn't work then give the library a folder and move it to a sub-directory and not the root of the drive, something like Z:\Library\ and try again.